A triangular number or triangle number counts the objects that can form an equilateral triangle One can define a function to compute the triangular number as: T(n) = 1 if n = 1 T(n) = n + T(n-1) if n > 1

Create a Lips function that calculate the triangular number, e.g., (defun triangular-number (x)) To test your Lisp program, calculate (triangular-number 5) & (triangular-number 6)